Traditional telephone sockets within home premises typically comprise a “master socket” and a number of extension sockets. Historically, the master socket is the point of demarcation for telephone services, which is to say that any wiring from the exchange up to and including the master socket is the domain of the service provider and any wiring beyond the master socket, including extension wiring, is the domain of the customer. In the UK, the master socket is typically a “NTE5” unit, where NTE is short for “network terminating equipment”. The NTE5 master socket allows a customer to easily add their own extension wiring within his premises, and also allows easy isolation of the main line from the extension wiring by removal of the front faceplate.
Digital Subscriber Line (DSL) technologies provide fast data connections, for example for broadband Internet access, over standard copper telephone lines. DSL utilizes transmission frequencies that are at a much higher frequency than those used for voice calls (“POTS”—plain old telephone service) on the copper lines. For example, the frequency band used in ADSL starts from about 25 kHz and finishes at just over 1000 kHz. In comparison, the frequency band for POTS stops at around 4 kHz. Whilst these frequencies are distinct from each other, interference can occur between POTS devices, such as telephones and fax machines, and DSL devices. As a result, filters are used to isolate the POTS signal from interference from DSL signals. The filters also provide isolation for the DSL transmissions from the POTS signals caused by transients generated during POTS signaling (e.g. dialing, ringing, off-hook etc).
Thus, the combined DSL and POTS telephone signal is low-pass filtered using what is usually referred to as a “microfilter”, so that voice frequencies (up to around 41 KHz) can pass through unaltered to a POTS output, but higher frequencies associated with DSL are filtered out. The combined signal is usually split by the process of filtering, so that there are usually two outputs: one filtered for POTS and one unfiltered for DSL.
ADSL microfilters are often installed as and when they are needed between a master or extension socket and any connected POTS device requiring isolation. However, there also exist specially adapted faceplates for master and extension socket NTE5 devices that incorporate a microfilter, which has both a filtered POTS connection (a standard phone connector socket) as well as an unfiltered data port for DSL connection (typically an RJ-11 connector socket for connection to a DSL modem). These special faceplates are usually referred to as “service specific front plate” or SSFP for short. SSFP devices can often provide enhanced broadband service by isolating the DSL signal from the POTS signal before the signal is presented to the extension wiring. The effect is particularly important for higher-frequency DSL, such as VDSL2, where the exclusion of such an SSFP can severely degrade the broadband service.
SSFPs are also used in other DSL installations, such as VDSL and VDSL2, which provide even faster data connections than ADSL. A VDSL2 SSFP will also separate out the voice telephony signals from the VDSL2 data signals. This is achieved through the use of band-pass or band-stop filters. The VDSL2 SSFP is designed such that the telephony signals will be filtered and provided at a telephony port and/or physically routed to any extension wiring; whilst unfiltered signals are presented at an extra data port exposed on the VDSL2 SSFP, to which a VDSL2 modem can be connected. FIG. 1 shows an example of a VDSL SSFP 100, with a filtered telephony port 102 and an unfiltered data port 104.
Whilst there are advantages to having a SSFP for VDSL2 (convenient data port, no need to use separate microfilters, improved signal isolation, etc), its installation also means that that an xDSL modem can no longer be connected to the POTS extension wiring, which has now been deliberately filtered to exclude high frequencies to overcome the issues highlighted above.
Therefore, if a premises is converted back to xDSL, such as ADSL, broadband connectivity (for example a new customer moving into the premises), then any xDSL modem will only work when connected to the additional data port 104 on the VDSL2 SSFP 100. This can cause a great deal of confusion for the new customer who will only be familiar with connecting his ADSL modem/router to the telephony port on a master/extension socket through a microfilter. The result would be numerous calls to the service providers helpdesk (which may or may not have knowledge of the presence of the VDSL2 SSFP), and may require an engineer visit to resolve who may remove the VDSL2 SSFP.
Additionally, it is known that whilst a SSFP will enable the provision of a better broadband service, a customer may be prepared to accept a lower broadband service, in exchange for the flexibility of connecting his VDSL2 modem to an extension socket. This is not possible with the SSFP design—for this configuration, a “data extension” cable must be run (perhaps physically alongside existing telephone extension wiring) to the preferred location of the VDSL2 modem. This can cause an unacceptable installation and management experience for the customer.